1. Field of the Invention
The present invention relates to a control device for a control motor of an internal combustion engine, and more particularly to a control device for a control motor of an internal combustion engine in which the control device causes the control motor to follow a target value obtained according to an engine operation state of the internal combustion engine.
2. Description of the Related Art
Since rpm changes and load changes in a vehicle engine are great, research has already been made into techniques which detect an operational state of the engine and control the opening and closing of a variety of control valves to achieve the optimum control in response to the operational state of the engine. For example, JP 62-126222 A describes a technique in which an exhaust control valve is provided near an open end on the downstream side of an exhaust pipe, and output increase is achieved by fully opening the control valve when the engine is in a high speed region, to utilize a dynamic effect of an exhaust system to a maximum limit on the one hand, and closing the control valve to approximately a xc2xd-opening degree to prevent the dynamic effect from operating in a reverse fashion in a medium speed region where a torque valley would be generated. A variety of proposals have also been made in which a control valve is provided to an interconnecting pipe connecting a plurality of intake pipes, and the control valve is caused to open and close with the engine rpm to essentially change the length of the intake pipe.
FIG. 5 shows one example of a method in which a motor controls these control valves so as to follow a target opening degree. In FIG. 5, reference numeral 100 indicates a target value computing means for computing a target value of an opening degree of the control valve (hereinafter, referred to as the target opening degree), reference numeral 101 indicates control information representing the engine""s operational state which is used in the computation of the target value by the target value computing means 100, reference numeral 102 indicates the target value computed by the target value computing means 100, and reference numeral 103 indicates a stop target area which is set at a given width with the target value as the center of the width. As shown in the flow chart in FIG. 6, in accordance with this method, first, a variety of sensors are used to detect the operational state of the engine which serves as control information, and from the control information the target value computing means 100 computes the target opening degree for the control valve that is the subject of the control (step S101). Then the current opening degree is computed (step S102), the stop target area is set around the computed target opening degree (step S103), and the current opening degree and the stop target area are compared (step S104). Then, if the current value is within the stop target area, the current value is kept (step S105), and if the current value is beyond the stop target area, a control is performed to output a motor control signal so as to bring the current value closer to the target value (step S106).
As described above, in the method in which the motor is used to control the control valve so that the control valve follows the target opening degree, the target opening degree is computed based on the control information indicating the engine""s operational state. Therefore, when an operation is performed to keep uniformly the control information, in a case where the control information has a characteristic that it always fluctuates, like engine rpm for example even when the operation is performed to uniformly maintain the control information, a phenomenon may occur in which the control valve and the motor which manipulates the control valve vibrate. This phenomenon occurs in the case where there is an area where the changes in the control information cause an amount of change xcex94xcex8 in the target opening degree to be greater than the width of the stop target area. This phenomenon occurs according to the sequence shown in FIG. 7. In FIG. 7, reference numeral 103 refers to the stop target area and reference numeral 104 refers to the current value. Portion (1) of FIG. 7 illustrates a state in which the motor current is turned off. In this state, the target opening degree fluctuates by an amount equal to xcex94xcex8. Along with this fluctuation, the stop target area 103 shifts in the forward rotational direction of the motor position by an amount equal to . . . , and enters the state shown in portion (2) of FIG. 7. In this state, the motor current flows so as to create a forward rotation, causing the current value 104 to shift in the forward rotational direction to enter the state shown in portion (3) of FIG. 7. In this state, another fluctuation in the control information causes the target opening degree to change, this time in the opposite rotational direction from the motor position, entering the state shown in portion (4) of FIG. 7. The motor current then flows to create a reverse directional rotation, thereby entering the state shown in portion (1) of FIG. 7. The above is performed repeatedly.
As described above, the setting of the target value and fluctuation of the control information that the target value is based on, work in a joint fashion, causing a phenomenon in which the motor vibrates. This phenomenon implies that a large starting current is flown to the motor again and again. Thus, there has been a problem in that the temperature of the motor increases excessively and the longevity of the motor is reduced.
The present invention has been made to solve the above-mentioned problems, and an object of the present invention is therefore to obtain a control device for a control motor of an internal combustion engine, which is capable of suppressing vibration of the control motor occurring when controlling the control motor for following a target value corresponding to an operational state of the engine.
The present invention relates to a control device for a control motor of an internal combustion engine, which follows a target value that changes in response to an operational state of the internal combustion engine, the control device including: control information output means for detecting the operational state of the internal combustion engine and outputting the same as control information; target value computing means for computing the target value of the operational state of the control motor according to the control information outputted from the control information output means; current value detecting means for detecting a current value of the operational state of the control motor; motor control signal determining means for generating a motor control signal for controlling a drive applied to the control motor, based on the target value and the current value; and drive means for driving the control motor based on the motor control signal, in which the motor control signal determining means has a parameter for determining the motor control signal to be outputted, and the value of the parameter is set by selecting one from among a plurality of values based on the control information.